title: Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge.
abstract: A novel charge-exchange recombination spectroscopy (CXRS) diagnostic method is presented, which uses a simple thermal gas puff for its donor neutral source, instead of the typical high-energy neutral beam. This diagnostic, named gas puff CXRS (GP-CXRS), is used to measure ion density, velocity, and temperature in the tokamak edge/pedestal region with excellent signal-background ratios, and has a number of advantages to conventional beam-based CXRS systems. Here we develop the physics basis for GP-CXRS, including the neutral transport, the charge-exchange process at low energies, and effects of energy-dependent rate coefficients on the measurements. The GP-CXRS hardware setup is described on two separate tokamaks, Alcator C-Mod and ASDEX Upgrade. Measured spectra and profiles are also presented. Profile comparisons of GP-CXRS and a beam based CXRS system show good agreement. Emphasis is given throughout to describing guiding principles for users interested in applying the GP-CXRS diagnostic technique.
authors.affiliation: MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Churchill
authors.forename: C
authors.initials: C
authors.lastname: Theiler
authors.forename: B
authors.initials: B
authors.lastname: Lipschultz
authors.forename: R
authors.initials: R
authors.lastname: Dux
authors.forename: T
authors.initials: T
authors.lastname: Pütterich
authors.forename: E
authors.initials: E
authors.lastname: Viezzer